Indications of flow near maximum compression in layered deuterium-tritium implosions at the National Ignition Facility

Abstract

An accurate understanding of burn dynamics in implosions of cryogenically layered deuterium (D) and tritium (T) filled capsules, obtained partly through precision diagnosis of these experiments, is essential for assessing the impediments to achieving ignition at the National Ignition Facility. We present measurements of neutrons from such implosions. The apparent ion temperatures T[subscript ion] are inferred from the variance of the primary neutron spectrum. Consistently higher DT than DD T[subscript ion] are observed and the difference is seen to increase with increasing apparent DT T[subscript ion]. The line-of-sight rms variations of both DD and DT T[subscript ion] are small, ∼ 150 eV, indicating an isotropic source. The DD neutron yields are consistently high relative to the DT neutron yields given the observed T[subscript ion]. Spatial and temporal variations of the DT temperature and density, DD-DT differential attenuation in the surrounding DT fuel, and fluid motion variations contribute to a DT T[subscript ion] greater than the DD T[subscript ion], but are in a one-dimensional model insufficient to explain the data. We hypothesize that in a three-dimensional interpretation, these effects combined could explain the results.